1. Field of the Invention
The present invention relates to a projection exposure device in which circuit patterns formed on a mask are projected to a surface of a film-shaped tape in high resolution. More particularly, the present invention is directed to a projection exposure device that does not occupy a large installation space, thereby contributing to efficient use of a space in a clean room.
2. Description of the Related Art
Recently, many circuit boards for electronic products are made of film-shaped tapes. Such film-shaped tapes are mainly applied to semiconductor integrated circuits or circuits formed by the tape automated bonding (TAB) technique. When film-shaped circuit boards are fabricated, the photolithography technique is typically utilized. This technique employs an exposure process for transferring circuit patterns to a surface of a board. A typical film-shaped circuit board is, for example, 0.05 mm or less thick and 200 m long. In this exposure process, circuit patterns must be transferred to the surface of a film-shaped board in resolution of less than 10 μm. Hence, this process is extremely difficult to conduct. In order to carry out this severe exposure process, a precise transfer device and a high-resolution optical system are required. Furthermore, the exposure process needs to be performed in a dustproof environment such as a clean room.
A film exposure device used in the exposure process has the following three types; a contact exposure type device which conducts the exposure process while a mask and a film-shaped board are kept in contact with each other; a proximity exposure type device which carries out the exposure process while a mask and a film-shaped board are arranged extremely close to one another; and a projection exposure type device which performs the exposure process while a mask and film-shaped board are not in contact and which attains the high resolution transfer.
FIG. 8 shows an example of a contact exposure type device (see JP-A2005-326550). This exposure device 201 has an exposure section 202 located at the center. The device 201 feeds a film-shaped board 203 downward for each block through the center of the exposure section 202, and then, moves photo-masks 204 and 204 in the X and Y directions while rotating them, so that they are aligned. Following this, optical sources 205 and 205 irradiate masks 204 and 204 with light. A supply reel 7 located on the right side feeds the film-shaped board 203, and a take-up reel 208 on the left side winds it.
A projection exposure device is configured to allow a projection exposure optical system to project an image of a reticle (mask) to a surface of a board, and to transfer this image to the surface. The device positions a board and maintains a distance between the reticle and the board with great precision.
JP-A62-293248 has introduced an example of a projection exposure device. This device uses a telecentric projection exposure system. In addition, the device moves a board vertically, and allows the telecentric projection exposure system to project and transfer patterns formed on the reticle to the surface of the board.
However, since the telecentric projection system is expensive, a device using a non-telecentric projection exposure system has been proposed. FIG. 9 schematically shows a projection exposure device equipped with a non-telecentric projection system (see JP2798158).
Referring to FIG. 9, a projection exposure device 210 is constituted by:
an optical source 211;
a reticle (mask) 212 placed on an optical axis of light from the optical source 211;
a non-telecentric projection system 213 for projecting the image on the reticle 212 to an upright projection plane;
a transfer mechanism 215 for feeding a film-shaped board 214 vertically for each block, and positions it on the projection plane;
a sensor 216 for sensing the horizontal displacement of the board 214 from the projection plane; and
a controller 217 for moving the reticle 212 and/or one or more lenses of projection system on the optical axis, based on the sensing result.
In the projection exposure device 210, the non-telecentric projection system 213 is placed such that its optical axis is parallel to a floor. Even if lenses making up the projection system 213 are displaced accidentally due to a mechanical error or environmental variation, the projection exposure device 210 can correct this displacement by moving the lenses and/or the reticle 212. Therefore, this device hardly causes errors during the exposure process.
In addition to the above device, a projection exposure device in which a non-telecentric projection system is placed vertically has been known.
On the other hand, JP2892079 has disclosed a method for pinching a tape-shaped board between a plate and an exposure stage in order to fix it firmly on the stage during the exposure process. In addition, JP2793000 has conceived a method for fixing a board on a circular exposure stage by using multiple electromagnetic valves.
However, such projection exposure devices have the following disadvantages.
In the exposure device 201 of JP-A2005-326550 as shown in FIG. 8, the film-shaped board 203 is fed from the supply reel 207 placed on the right side, and is wound by the take-up reel 208 placed on the left side. Thus, since the transfer mechanism has a long lateral length, its installation space ends up large.
In the projection exposure device of JP2798158 as shown in FIG. 9, the optical axis of the non-telecentric projection system 213 extends laterally. Therefore, it needs to occupy a large lateral space. As far as judging from FIG. 9, the projection system 213 of FIG. 9 does not seem to occupy such a large space. However, in fact, the projection system is made up of 20 lenses or so in order to achieve high resolution. Thus, its lateral length reaches 2.5 m or more. Hence, there needs to be a large space in a clean room to install this device.
Also, the projection exposure device of JP-A62-293248, which is the telecentric projection exposure system, is difficult to shrink.
Even if a non-telecentric projection system is installed in an upright position, its installation space does not shrink. This is because the transfer mechanism for transferring a board is, in turn, enlarged laterally. In addition, since standing high, the system may block air flow, so that environment in a clean room is worsened.
On the other hand, a board tends to be thinner for the purpose of enhancing the performance of an electronic circuit board. As a board is thinner, the board is more likely to be warped due to stress or variation in temperature or moisture during a fabrication process. In the exposure process, a resist is applied to the surface of a board, and the board is then baked. Hence, a board inevitably undergoes stress due to thermal expansion and contraction. In addition, when a board is fed from a reel, the board is subjected to different environment. Then, the board may be warped between its center and both side edges or between the center and areas outside perforations.
Suppose the case where a warped board is fixed to an exposure stage. Although the center of this board is in contact with the exposure stage, its both edges may float off the stage. In this case, the board cannot be fixed thereon firmly, which may affect the exposure process.
In order to overcome this disadvantage, JP-A2892079 has disclosed a structure where a plate presses a board against an exposure stage. However, in this structure, a board may be damaged. In addition, even if a board is pressed, it does not always keep in surface contact with an exposure stage. In fact, it may partially float off the stage.
Taking the above disadvantages, the present invention has been conceived. An object of the present invention is to provide a projection exposure device having a small volume, thereby not occupying a large installation space. An additional object of the present invention is to present projection exposure device and process, by which a board can make surface contact with an exposure stage.